Subzero: Rewrite the pass timing infrastructure.

src/IceTargetLowering.cpp

Index: src/IceTargetLowering.cpp
diff --git a/src/IceTargetLowering.cpp b/src/IceTargetLowering.cpp
index f6631559f9064a5049c842b74ba441c47da88b24..90ef7a54eae132307f1a3bd093c1c7850a7fcd06 100644
--- a/src/IceTargetLowering.cpp
+++ b/src/IceTargetLowering.cpp
@@ -229,6 +229,7 @@ void TargetLowering::lower() {
 // registers could potentially be parameterized if we want to restrict
 // registers e.g. for performance testing.
 void TargetLowering::regAlloc() {
+  TimerMarker T("regAlloc", Ctx);
   LinearScan LinearScan(Func);
   RegSetMask RegInclude = RegSet_None;
   RegSetMask RegExclude = RegSet_None;